Preparation of maleic anhydride from four-carbon hydrocarbons

ABSTRACT

Maleic anhydride is produced by the oxidation of n-butane, n-butenes, 1,3-butadiene or mixture thereof with molecular oxygen in the vapor phase in the presence of a catalytic oxide of molybdenum, phosphorus, rubidium, oxygen, and at least one element selected from the group consisting of Sn, rare earth element, Ni, Zr, Ba, Fe, Rh, Mn, Re, Ru, Co and Cu.

BACKGROUND OF THE INVENTION

Belgian Pat. No. 828,074 discloses that catalysts containing phosphorus, molybdenum, bismuth, copper, oxygen, at least one element selected from the group consisting of Fe, Co, Ni, and at least one element selected from the group consisting of Li, Na, Bi, Cs, Be, Mg, Sr and Ba are useful in the preparation of maleic anhydride from butene-1, butene-2, butadiene, pentane, pentadiene, cyclopentadiene and benzene.

SUMMARY OF THE INVENTION

It has now been discovered according to the present invention in the process for the production of maleic anhydride by the oxidation of n-butane, 1,3-butadiene, n-butenes or mixtures thereof, with molecular oxygen in the vapor phase at a reaction temperature of about 250° C to about 600° C in the presence of a catalyst, and optionally in the presence of steam, the improvement which comprises using as a catalyst a catalyst described by the formula

    X.sub.a Mo.sub.12 P.sub.b Rb.sub.c O.sub.x

wherein

X is at least one element selected from the group consisting of Sn, rare earth element, Ni, Zr, Ba, Fe, Rh, Mn, Re, Ru, Co and Cu; and wherein

a is a positive number less than about 20;

b and c are numbers from 0.001 to 10;

x is the number of oxygens required by the valence states of the other elements present.

Especially high yields and selectivities of maleic anhydride are obtained from four-carbon hydrocarbons in an efficient, convenient, and economical manner at a relatively low temperature.

The most significant aspect of the present invention is the catalyst employed. The catalyst may be any of the catalysts delineated by the above formula. Preferred catalysts within the formula are described wherein a is a positive number less than about 12; catalysts wherein b is 0.01 to 5; and catalysts wherein c is 0.01 to 5. Especially preferred catalysts are described wherein b is 0.5 to 1.5 and c is 0.1 to 1.0. Highly desirable catalysts are described wherein X is at least one element selected from the group consisting of Ni, Cu, Sn, and a rare earth element.

The methods of preparing the catalysts of the present invention may vary widely. A number of techniques are known to those skilled in the art. Methods of catalyst preparations such as coprecipitation, evaporative drying, or oxide mixing, followed by calcining the resulting catalysts may be successfully employed.

The preferred procedure of this invention involves preparing the catalysts in an aqueous slurry or solution of compounds containing molybdenum and phosphorus, adding the remaining components; evaporating this aqueous mixture; and calcining the resulting catalysts. Suitable molybdenum compounds that may be employed in the preparation of the catalysts delineated by the above formula include molybdenum trioxide, phosphomolybdic acid, molybdic acid, ammonium heptamolybdate, and the like. Excellent results are obtained using catalysts of the invention wherein at least part of the molybdenum employed in the preparation of the catalysts is supplied in the form of molybdenum trioxide.

Suitable phosphorus compounds that may be employed in the preparation of the catalysts include orthophosphoric acid, metaphosphoric acid, triphosphoric acid, phosphorus halides, and phosphorus oxyhalides. The remaining components of the catalysts may be added as oxide, acetate, formate sulfate, nitrate, carbonate, halide and oxyhalide.

The catalysts of this invention also may be prepared by mixing the catalytic components in an aqueous slurry or solution, heating the aqueous mixture to dryness; and calcining the resulting catalysts.

The best results are obtained by refluxing phosphoric acid and molybdenum trioxide or ammonium heptamolybdate in water for about 0.5 to 3 hours, however, commercial phosphomolybdic acid may be effectively utilized; adding a compound containing rubidium compounds containing elements delineated by X to the aqueous slurry and boiling to a thick paste; and drying the resulting catalysts at 110° to 120° C in air.

By the preferred procedure of the invention, calcination of the catalysts is not generally required to obtain desired catalysts described within the above formula. However, calcination of particular catalysts of the invention may be accomplished by heating the dry catalytic components at a temperature of about 300° to about 700° C; preferred calcination is accomplished at a temperature of 325° to 450° C. The hydrocarbon reacted may be n-butane, n-butenes, 1,3-butadiene or mixture thereof. Preferred is the use of n-butenes, or a mixture of hydrocarbons that are produced in refinery streams. The molecular oxygen is most conveniently added as air, but synthetic streams containing molecular oxygen are also suitable. In addition to the hydrocarbon and molecular oxygen, other gases may be added to the reactant feed. For example, steam or nitrogen could be added to the reactants.

The ratio of the reactants may vary widely and are not critical. The ratio of the hydrocarbon to molecular oxygen may range from about 2 to about 30 moles of oxygen per mole of hydrocarbon. Preferred oxygen ratios are about 4 to about 20 moles per mole of hydrocarbon.

The reaction temperature may vary widely and is dependent upon the particular hydrocarbon and catalyst employed. Normally, temperature of about 250° to about 600° C are employed with temperature of 250° to 450° C being preferred.

The catalyst may be used alone or a support could be employed. Suitable supports include silica, alumina, Alundum, silicon carbide, boron phosphate, zirconia, and titania. The catalysts are conveniently used in a fixed-bed reactor using tablets, pellets or the like or in a fluid-bed reactor using a catalyst preferably having a particle size of less than about 300 microns. The contact time may be as low as a fraction of a second or as high as 20 seconds or more. The reaction may be conducted at atmospheric, superatmospheric or subatmospheric pressure.

Excellent results are obtained using a coated catalyst consisting essentially of an inert support material having a diameter of at least 20 microns and an outer surface and a continuous coating of said active catalyst on said inert support strongly adhering to the outer surface of said support.

By use of these coated catalysts in the reaction to produce maleic anhydride, a very low exotherm is realized allowing for better control of the reaction. High single pass yields are exhibited and the elimination of undesirable byproducts is obtained.

The special coated catalyst consists of an inner support material having an outside surface and a coating of the active catalytic material on this outside surface. These catalysts can be prepared by a number of different methods.

The support material for the catalyst forms the inner core of the catalyst. This is an essentially inert support and may have substantially any particle size although a diameter of greater than 20 microns is preferred. Especially preferred in the present invention for use in a commercial reactor are those supports which are spherical and which have a diameter of about 0.2 cm. to about 2 cm. Suitable examples of essentially inert support materials include: Alundum, silica, alumina, alumina-silica, silicon carbide, titania and zirconia. Especially preferred among these supports are Alundum, silica, alumina and alumina-silica.

The catalysts may contain essentially any proportions of support and catalytically active material. The limits of this relationship are only set by the relative ability of the catalyst and support material to accommodate each other. Preferred catalysts contain about 10 to about 100 percent by weight of catalytically active material based on the weight of the support.

The preparation of these coated catalysts can be accomplished by various techniques. The basic method of preparing these catalysts is to partially wet the support material with a liquid. The support should be wet on the outside surface of the total mass. It should appear to be dry to the touch. If the support is wet, then the active catalytic material will agglomerate into separate aggregates when coating of the support is attempted. These partially wet supports are then contacted with a powder of the catalytically active material and the mixture is gently agitated until the catalyst is formed. The gentle agitation is most conveniently conducted by placing the partially wet support in a rotating drum and adding the active catalytic material until none is taken up by the support. This is very economically done.

Using the catalysts of the invention in the preparation of maleic anhydride, excellent yields are obtained in a convenient reaction with low amounts of byproducts.

SPECIFIC EMBODIMENTS

A catalyst of the formula Ni₀.2 Cu₀.25 Mo₁₂ P₁.32 Rb₂ O_(x) was prepared as follows:

A slurry was prepared of 86.4 grams (0.6 mole) of molybdenum trioxide and 7.7 grams (0.067 mole) of 85% phosphoric acid in 800 mls. of distilled water; boiled with stirring for two hours which was yellow greenish in color. 0.74 grams (0.01 mole) of nickel oxide were added to the slurry; no change in color, followed by the addition of 2.49 grams (0.0125 mole) of copper acetate hydrate and no change in color was observed. Boiling was continued for an additional 1.5 hours, heating was discontinued, distilled water was added to the mixture to bring the volume up to 800 mls., and the slurry was allowed to stir overnight. The next day 14.4 grams (0.1 mole) of rubidium acetate were added and a heavy yellow precipitate immediately formed. This mixture was boiled to a thick paste and dried in an oven at 110°-120° C. overnight. The catalyst was ground and screened to 20/30 mesh size.

The reactor was constructed of a 1.02 cm. inside diameter stainless steel tube. A portion of the catalyst fraction was charged to the 20 cc. reaction zone of the reactor.

The reactor was heated to reaction temperature and a feed of air/butene-2, as indicated below, was fed over the catalyst at an apparent contact time of 1.0 to 1.5 seconds and the performance was evaluated by collecting and analyzing the products.

The results of the experiments appear in the Table below. The following definitions are used in measuring the carbon atoms in the feed and in the product: ##EQU1##

PREPARATION OF MALEIC ANHYDRIDE FROM 1,3-BUTADIENE

In the same manner described above, the catalyst Ni₀.2 Cu₀.25 Mo₁₂ P₁.32 Rb₂ O_(x) was reacted with air and 1,3-butadiene. An air/1,3-butadiene feed of 84/1 was passed over the catalyst at a reaction temperature of 285° C at an apparent contact time of 1.5 seconds. The results of this experiment showed a 17.8% single pass yield of total acid.

                                      TABLE                                        __________________________________________________________________________     PERFORMANCE OF THE CATALYST Ni.sub.0.2 Cu.sub.0.25 Mo.sub.12 P.sub.1.32        Rb.sub.2 O.sub.x                                                               IN THE PRODUCTION OF MALEIC ANHYDRIDE FROM BUTENE-2                            Hours On                                                                             Air/HC                                                                               Temp. ° C                                                                               Results, %                                         Stream                                                                               Feed Ratio                                                                           Bath                                                                              Exotherm                                                                             Total Acid                                                                            Maleic Anhydride                                   __________________________________________________________________________     0.7   92    375                                                                               418   39.3   35.8                                               3.3   96    340                                                                               386   43.8   39.5                                               5.0   96    299                                                                               322   44.5   32.5                                               24.0  91    315                                                                               343   50.3   34.2                                               26.5  91    308                                                                               337   48.9   32.6                                               28.0  120   304                                                                               331   45.2   35.1                                               46.0  106   317                                                                               366   49.1   37.3                                               46.0  93    302                                                                               319   48.1   43.6                                               __________________________________________________________________________ 

We claim:
 1. In the process for the production of maleic anhydride by the oxidation of n-butane, 1,3-butadiene, n-butenes or mixture thereof, with molecular oxygen in the vapor phase at a reaction temperature of about 250° to about 600° C in the presence of a catalyst, and optionally in the presence of steam, the improvement comprising using as a catalyst a catalyst of the formula

    X.sub.a Mo.sub.12 P.sub.b Rb.sub.c O.sub.x

wherein X is at least one element selected from the group consisting of Sn, rare earth element, Ni, Zr, Ba, Fe, Rh, Mn, Re, Ru, Co and Cu; and wherein a is a positive number less than about 20; b and c are numbers from 0.001 to 10; x is the number of oxygens required by the valence states of the other elements present.
 2. The process of claim 1 wherein a is a positive number less than about
 12. 3. The process of claim 1 wherein b is 0.01 to
 5. 4. The process of claim 1 wherein c is 0.01 to
 5. 5. The process of claim 1 wherein b is 0.5 to 1.5 and c is 0.1 to 1.0.
 6. The process of claim 1 wherein X is at least one element selected from the group consisting of Ni, Cu, Sn, and a rare earth element.
 7. The process of claim 1 wherein X is nickel and copper.
 8. The process of claim 1 wherein n-butenes are reacted.
 9. The process of claim 1 wherein 1,3-butadiene is reacted. 